fi has a bit of a strange history. Formally, it is part of the Fixed Point Designer toolbox, and you need that toolbox in order to use it in some circumstances. But fi is also generated by Simulink in other circumstances even without the Fixed Point Designer toolbox, and the documentation indicates that you should be able to use fi for those particular operations even without the Fixed Point Designer toolbox. The documentation is weak on this point and I have been left uncertain about whether it will work or not.
As Image Analyst indicates, you should use ver to check for the Fixed Point Designer. In particular,
will tell you directly whether you have it installed. But you also need to find out whether it is licensed; for that check
and also use
and if it returns something look towards the end of the line to see whether it says anything about a missing license.